1. Field of the Invention
The present invention relates to charged particle beam apparatus, such as scanning electron microscopes, electron beam exposure apparatus, ion implantation apparatus and other semiconductor manufacturing apparatus which irradiate wafers and other specimens with electron beams, ion beams and other charged particle beams.
2. Description of the Related Art
In charged particle beam apparatus, such as scanning electron microscopes, various methods have so far been used to prevent a specimen from being charged by electron beam irradiation. One of them is to cover the specimen with a metal or other conductive thin film.
In addition, for such scanning electron microscopes as CD-SEM, it is proposed to set up a nozzle near the specimen within the chamber as disclosed in Japanese Patent Laid-Open No. 2005-235777 and Japanese Patent Laid-Open No. 2004-327302. In this technique, N2, Ar, O3 or other gas is supplied onto the specimen in order to avoid the charging up of the specimen.
However, in the case of semiconductor manufacture, if a wafer under examination is coated with metal or the like, this wafer can not directly be put into the subsequent process. Likewise, if a mask under examination is coated with a conductive thin film, a process of removing this thin film is necessary. If the removal process is imperfect, the thin film would leave residuals as defects.
In addition, a typical recent high resolution electron optical system has a retarding electric field between the specimen and the objective lens as disclosed in Japanese Patent No. 30149986 and Japanese Patent Laid-Open No. 2003-187733. In such an electron optical system, a gas emission nozzle can not be disposed near the specimen below the objective lens since discharge would occur.
To raise the resolution of an electron optical system, it is also necessary to shorten the work distance. Therefore, it is sometimes impossible to dispose a nozzle between the specimen and the bottom of the electron optical system as disclosed in Non-Patent Document 1.
Further, as disclosed in a figure of “Charging Reduction in a Review SEM by Local Gas Injection” (LSI Testing symposium 2005 proceeding, 2005. 11. 9-11) (see FIG. 9), gas injection poses a problem that the resolution of the charged particle optical system deteriorates according as the degree of vacuum deteriorates apart from the disadvantage that the apparatus becomes larger in scale due to the gas introduction system and vacuum control.